1. Field of the Invention
The present invention relates to an image processor and an image processing method, and more particularly, to an image processor and an image processing method that carry out image processing of document image data that is formed from a plurality of pixel data that are generated due to shooting of a document image.
2. Description of the Related Art
Recently, there has been an enhancement in image quality, enhancement in performance, and a reduction in cost of a two-dimensional image sensor that is included in a digital camera or a mobile camera such as a camera that is mounted on a mobile phone. The two-dimensional image sensor is normally used in photography. Further, due to increasingly high image quality and increasingly high performance of the two-dimensional image sensor, the two-dimensional image sensor can also be used to shoot or capture a document image such as a paper document, characters written on a blackboard or a white board of a meeting room, a newspaper sheet, a magazine etc. and character data of the document image can be saved as document image data.
In the document image data, which is formed from a plurality of pixel data that are generated due to shooting of the document image by the two-dimensional sensor, readability is more important than loyally reproducing an imaging target object such as scenery or a person. However, because the mobile camera is not used by prior setting conditions such as a position of a user, luminous surroundings, an imaging target etc., the document image data is not always readable.
For shooting the document image using the mobile camera and enhancing the readability of the generated document image data, an existing technology is suggested that carries out image processing using shading correction. For example, in the existing technology disclosed in Japanese Patent Application Laid-open No. 2005-269451, the document image data, which is formed from the multiple pixel data that are generated due to shooting of the document image, is converted into luminance image data that includes a luminance component. Each pixel data of the converted luminance image data is split into a plurality of blocks that include the same number of pixel data. Based on a maximum luminance value among each pixel data of each block, shading correction of each block pixel data is carried out, thus performing image processing.
The imaging target, which is the document image, may also include a material such as a book that is originally a flat surface but does not remain as a flat surface in a readable condition. In other words, the mobile camera is also used to shoot the document image that is originally in the form of a flat surface but does not remain as a flat surface in an imaged condition. Accordingly, because the document image is not a flat surface in the imaged condition, the document image data, which is generated by shooting with the mobile camera, the document image that is not a flat surface in the imaged condition, is likely to become difficult to read. Further, in another existing technology disclosed in Japanese Patent Application Laid-open No. H5-161002, an imaging sensor (the two-dimensional image sensor) is used to shoot the document image that is originally a flat surface but is not a flat surface in the imaged condition. The generated document image data is expanded to a flat surface.
However, in the existing technology disclosed in Japanese Patent Application Laid-open No. 2005-269451, if the document image data includes black pixel data or highlighted pixel data to some extent, luminous unevenness cannot be sufficiently curbed even after carrying out the shading correction. Due to this, if the document image data includes the black pixel data or the highlighted pixel data to some extent, the document image data after the image processing is not sufficiently readable. Further, in the existing technology disclosed in Japanese Patent Application Laid-open No. H5-161002, limiting a distance between the two-dimensional image sensor and the imaging target enables to expand the generated document image data to a flat surface. However, because the distance between the two-dimensional image sensor and the imaging object cannot be grasped in the mobile camera, such a technique is difficult to apply to the document image data that is generated using the mobile camera. Thus, it is difficult to enhance the readability of the document image data that is generated based on the document image that is shot using the two-dimensional image sensor and that is originally a flat surface but is not a flat surface in the imaged condition.